This invention relates to environmentally acceptable stabilized vinyl chloride polymer compositions from which environmentally objectionable metals such as arsenic, cadmium, beryllium, lead, mercury, and thallium are substantially excluded, and to an anti-yellowing additive to such environmentally acceptable stabilized vinyl chloride polymer compositions to minimize undesirable yellowing during the process of fabricating and shaping such compositions into useful articles.
There is a voluminous literature on the stabilization of vinyl chloride polymers. Patent disclosures of materials stated to be useful in minimizing deterioration of vinyl chloride polymers on heating number well over one thousand. Among the more important heat stabilizers in commercial use are mild alkalis such as sodium carbonate, disodium phosphate, and sodium and potassium salts of partially esterified phosphoric acids; carboxylates and phenolates of zinc, cadmium, and the alkaline earth metals; inorganic and organic lead salts; organotin carboxylates as disclosed by Quattlebaum in U.S. Pat. No. 2,307,157; organotin mercaptides as disclosed by Leistner in U.S. Pat. Nos. 2,641,588 and 2,641,598; various metal-free organic compounds such as the polyols, e.g. mannitol, sorbitol, glycerol, pentaerythritol, organic phosphites, 1,2-epoxides, e.g., soybean oil epoxide, isooctyl epoxy-stearate, and diglycidyl ether of 2,2-bis(p-hydroxyphenyl) propane, and nitrogen compounds, e.g., phenylurea, N,N'-diphenylthiourea, and 2-phenylindole. For detailed discussion of heat stabilizers for vinyl halide resins, reference may be made to the articles, L. I. Nass, in "Encyclopedia of Polymer Science and Technology" (N. Bikales, ed.) Vol. 12, pages 737 to 768 (1970); N. L. Perry "Barium-Cadmium Stabilization of Polyvinyl Chloride, "Rubber Age 85 449-452 (June, 1959), and by H. Verity-Smith, British Plastics 27 176-179, 213-217, 307-311 (1954); the brochure by the same author The Development of the Organotin Stabilizer (Tin Research Institute, 1959) and the book La Stabilisation des Chlorures de Polyvinyle by F. Chevassus (Amphora, Paris, 1957).
Preponderant in quantity used for many years have been the lead salts, such as tribasic lead sulfate, normal and dibasic lead stearate, dibasic lead phthalate, dibasic leadphosphite, and basic lead carbonates and silicates. Vinyl chloride polymer compositions stabilized with lead compounds are recognized as outstanding in electrical properties and good in color protection during long extended processing at high temperatures, while poor in clarity owing to the insolubility and pigmenting properties of the lead compounds. Next in quantity used have been the organic salt mixtures containing cadmium, as disclosed for example by W. Leistner, in U.S. Pat. No. 2,716,092 of Aug. 23, 1955, G. Mack in U.S. Pat. No. 2,935,491, of May 23, 1960 and J. Scullin in U.S. Pat. No. 3,390,112 of June 25, 1968. Cadmium containing stabilizers have provided excellent heat stability combined with outstanding clarity and resistance to weathering exposure. With the steady increase in usage of vinyl chloride polymer compositions and coincidentally increased concern about the accumulation of toxic materials in the human environment, there has developed a need to replace the lead and cadmium based stabilizers by environmentally more acceptable and no less effective stabilizers. The very favorable properties of the lead and cadmium containing stabilizers, however, have made it difficult to find equivalent replacements. In particular, vinyl chloride polymer compositions stabilized with materials other than lead and cadmium have been subject to objectionable yellowing even where the time to severe heat failure was relatively satisfactory.
Many organic phosphites have been proposed as stabilizers for polyvinyl chloride resins, and are employed either alone or in conjunction with other stabilizing compounds, such as polyvalent metal salts of fatty acids and alkyl phenols. Such phosphite stabilizers normally contain alkyl or aryl radicals in sufficient numbers to satisfy the three valences of the phosphite. Typical phosphites are described, for example, by W. Leistner et al in U.S. Pat. Nos. 2,564,646 of Aug. 14, 1951 and 2,997,454 of Aug. 2, 1961, and by L. Friedman et al in U.S. Pat. Nos. 3,047,608 of July 31 and 3,053,878 of Sept. 11, 1962.
J. Darby in U.S. Pat. No. 2,669,548 of Feb. 16, 1954 disclosed halogen-containing resin compositions having improved stability containing a mixture of a zinc salt and a calcium chelate derivative of a 1,3-dicarbonylic compound capable of keto-enol tautomerism. Zinc salts can be zinc salts of organic acids and zinc salts of weak inorganic acids, for example zinc acetate, zinc propionate, zinc octanoate, zinc ricinoleate, stearate, and zinc salts of carbonic, silicic, and boric acids. Calcium chelates can be derivatives of betadiketones, beta-ketoacids, and the esters of betaketoacids, for example the calcium chelates of ethyl acetoacetate, phenyl acetoacetate, acetoacetic acid, acetylaceton, benzoylaceton, and diacetylaceton. In U.S. Pat. No. 3,346,536 of Oct. 10, 1967 there is disclosed a stabilizer combination of a ketoacetic acid compound, which can be an ester or an acid anhydride dimer thereof, with a metal salt of an organic acid. The ketoacetic acid esters have the formula ##STR2## wherein R is an inert organic group having from one to about thirty carbon atoms, R' is an inert organic radical having from one to about thirty carbon atoms, and x is a number from one to ten. The ester molecule has a total of at least eight carbon atoms.
The ketoacetic acid anhydride dimers have the formula ##STR3## R is again as above and R.sub.1 is hydrogen or R'.
It is further disclosed that this stabilizer combination can be used with additional heat stabilizers, among which phenols and organic triphosphites and acid phosphites are preferred. Many useful phosphites are disclosed at Column 9 line 16 to Column 10 line 13.